The present invention relates to an electromagnetic drive device in which a magnet rotor formed of permanent magnet is rotatably accommodated in a coil frame with a coil wound around an outer periphery thereof so that the magnet rotor rotates when a direct current is supplied to the coil, and a light quantity adjustment device for adjusting a light quantity of an optical image pick-up device with a torque generated by the magnet rotor.
Generally, as disclosed in Japanese Utility Model No. 2606159, in an optical device such as a video camera and a still camera, a shutter blade member is provided in a lens-barrel with an image pick-up lens for blocking light or a stop blade member is provided for adjusting a quantity of light. The blade member is incorporated in the lens-barrel on an image pick-up optical axis to be rotatable or slidable, and is controlled by an electromagnetic drive device.
In such an electromagnetic drive device, a magnet rotor is rotatably accommodated inside a coil frame with a conductive coil wound around an outer periphery thereof, and a rotation of the magnet rotor is transmitted to the blade member to adjust the photographing optical axis by increasing and decreasing an aperture diameter. There has been widely used a structure in which a magnet rotor is polarizes in two poles N and S, and a magnetic field is generated in the coil to rotate the rotor when a direct current is supplied to a coil.
In the electromagnetic drive device, the hollow tubular coil frame is formed of a resin and so forth, and the magnet rotor having a rotational shaft is rotatably supported and accommodated in the coil frame. A torque is transmitted to the blade member from the rotational shaft through a transmission arm. The coil frame has a structure divided into two portions so that the magnet rotor is accommodated therein. After the rotor is accommodated in the coil frame, the two portions are joined, and the coil is wound around an outer periphery of the coil frame. The coil frame may be divided left and right into two portions in a longitudinal direction through the rotational shaft of the magnet rotor or may be divided laterally up and down into two portions in a direction perpendicular to the rotational shaft.
When the coil frame is divided left and right into two portions in a longitudinal direction, the coil can not be wound around a joint line (connection surfaces) of the two coil frame halves, so that a coil winding part is provided in each of the two coil frame halves for winding the coil. Accordingly, the coil is wound around each of the coil winding parts except the connection surfaces at a center of the coil frame, thereby increasing a size of the device.
The invention is directed to an improved structure of a coil frame laterally divided up and down into two portions as disclosed in Japanese Utility Model No. 2606159, while solving a problem described above. In the conventional device, after the cup-shaped coil frame halves divided up and down into two portions are joined, the magnet rotor is accommodated in a hollow tube portion of the coil frame, and the coil is wound around an outer periphery of the coil frame, thereby integrally assembling the device. The magnet rotor is integrally provided with a rotational shaft at a center of a cylindrical magnet, and the rotational shaft is supported through bearing holes formed in the coil frame halves. A transmission arm is attached to the rotational shaft of the magnet rotor in a direction perpendicular to the rotational shaft, and protrudes to an outside from an opening formed in a peripheral side surface of the coil frame.
As described above, when the coil frame halves formed in the cup-shaped shape are joined and the transmission arm perpendicularly attached to the rotational shaft of the magnet rotor protrudes from the peripheral side surface to the outside, there is the following problem. Conventionally, as disclosed in Japanese Utility Model No. 2606159, concave notch parts are provided in the joint surfaces (connection surfaces) of the coil frame halves, and a window opening is formed of the two notch parts, so that the transmission arm protrudes to the outside. However, when joint portions (contact portions) and the notched portions (window opening) are provided in the joint surfaces (flange parts) of the coil frame halves, a positional misalignment tends to occur when the two coil frame halves are joined. Especially, a size of the device has been reduced recently, and a diameter of the coil frame has been reduced to 4 mm. Accordingly, the joint portions of the coil frame halves have been reduced to about 8 mm, so that it is difficult to accurately join the coil frame halves.
In addition to such a problem, when the coil wound around the outer periphery of the coil frame is contracted due to a change in an ambient temperature or with time, a strong tightening force is applied to the concave notch portions. Accordingly, a shape of the opening deforms to reduce an operational range of the transmission arm, so that the shutter blade may not be closed completely, or the stop device may not set a light quantity correctly.
These problems are apparent when a device has a coil frame with a thickness of about 1 mm. When the coil wound around the outer periphery of the coil frame is contracted due to a change in an ambient temperature or an impact applied on the coil in use, a shape of the opening deforms.
In view of the problems described above, an object of the invention is to provide an electromagnetic drive device in which coil frame halves are joined without a positional misalignment and an operational range of the transmission member is not reduced by the structure such that joint portions of coil frame halves and an opening for protruding a transmission arm outwardly are formed at different locations.
Another object of the invention is to provide a light quantity adjustment device such as a shutter device and a stop device, in which an operation thereof is not affected by an external impact or a change in an ambient temperature.
Further objects and advantages of the invention will be apparent from the following description of the invention.